Dropping boiler pressure & leaking radiator pipe... link

Hi all - hope everyone's enjoying the sunshine!

My boiler ( Vaillant VCW sine 18) is losing pressure over 24 hrs - i top it up to 1.5 bars, and it drops by the next day

There is a small drip from bottom of a red tank thing (i assume it's the expansion tank) but today i also noticed a leak from one of my rads (pics attached). It has a pipe coming out of the main imlet pipe to rad and there's a slow drip.leak from there - should i just tighten that square thing sticking out of it???
Any ideas about how to stop the boiler pressure loss please? Or is it just my pressure gauge???

Ironically, it's not affecting performance - heating works fine, as does hot water, and when either HW or CH is on, pressure needle rises to 1 bar, from zero.

Any ideas / help would be appreciated.

Thank you
Marios

Thats your radiator drain off valve for your rads. You could try to tighten it a little. This red tank you speak of, have you taken the cover off your boiler to find this? If its leaking from your expansion tank then thats bad news! Where abouts is the leak?
Your boiler is losing pressure because your losing water from your rads...

//www.diynot.com/forums/viewtopic.php?p=251090#251090 the expansion vessel needs sorting, check out this link

thanks guys!